The objective of this proposal is to explore the nature of baroreceptor influences on endocrine function in the conscious animal. The focus is on the neurohypophyseal axis since evidence shows that there is a reciprocal relationship between baroreceptor nerves and central peptidergic systems. Experiments are designed to test the hypothesis that baroreceptor input has inhibitory effects on vasopressin and oxytocin secretion which are mediated by brain stem noradrenergic input. Sinoaortic denervation will be used as the model, to probe the effect of removal of afferent input on the peptidergic systems. The specific aims are : 1) to determine the effect of baroreceptor denervation on cardiovascular and endocrine function in the conscious rat. The time course of the changes in plasma vasopressin and oxytocin and cardiovascular parameters will be evaluated; 2) to evaluate hormonal and cardiovascular responsiveness in the baroreceptor denervated animal using paradigms in which secretion is stimulated or inhibited; 3) to examine the changes in central responsiveness in the denervated animal using an in vivo microdialysis system for the delivery of stimuli to the paraventricular and supraoptic regions; 4) to determine the mechanisms by which baroreceptor input alters peptide secretion by evaluating the effects of brain stem or hypothalamic lesions and selective neural denervation on endocrine and cardiovascular responses; and 5) to examine the hypothalamic/brain stem interactions by determining the influence of specific lesions of the parvicellular region of the paraventricular nucleus. This investigation will provide information on the interactions between the autonomic nervous system and the endocrine hypothalamus which are critical in cardiovascular fluid/electrolyte balance.